1. Field of the Invention
The present invention relates to a panoramic/cephalo X-ray photographing device for photographing the entire jaws (hereafter referred to as "panoramic photographing") which can also be used for photographing a standardized head section (cephalometric radiography . . . hereafter referred to as "cephalo photographing").
2. Prior Art
Dental X-ray photographing devices are generally classified into three types: a panoramic X-ray photographing type, a cephalo X-ray photographing type and a dental X-ray photographing type. These days, the device of the cephalo X-ray photographing type has become very important for orthodontics treatment, for example. The device of this type is large and expensive, however. Therefore, installing the device of this type together with a panoramic X-ray photographing device, which is indispensable for dental treatment, is very difficult because of space and cost. To solve this problem, a dental panoramic/cephalo X-ray photographing device capable of performing both panoramic and cephalo photographing has been developed and come into practical use.
The general structure of the above-mentioned panoramic/cephalo X-ray photographing device is described below referring to FIG. 1 illustrating an example of the present invention. The device generally comprises a stay 7, an arm support member 12 installed on the stay 7, a horizontal rotary arm 1 supported rotatably in the horizontal direction by the arm support member 12, an X-ray generator 2 supported on one end of the rotary arm 1, a panoramic film cassette 8 supported on the other end of the rotary arm 1, a support 9 horizontally extended from the stay 7 and equipped with a cephalo photographing film cassette 91 provided at the front end of the support 9. Numeral 11 represents a patient securing means for panoramic photographing. The rotary arm 1 rotates around the patient's head secured by the securing means 11. As the rotary arm 1 rotates, X-ray is irradiated from the X-ray generator 2 and a tomographic panoramic photographing image of a dental arch is obtained on the film cassette 8. Numeral 92 represents a patient securing means for cephalo photographing. X-ray is irradiated from the X-ray generator 2 to the patient's head secured by the patient securing means 92 and a standardized head section photographing image is obtained on the film cassette 91.
To select the panoramic/cephalo photographing modes of the above-mentioned device, the following two methods are generally used.
i) The X-ray generator 2 is made rotatable horizontally and the X-ray irradiation axis of the X-ray generator 2 is directed to the panoramic photographing film cassette 8 or the cephalo photographing film cassette 91 depending on the photographing mode. (JAP. UM Publication with Examined Contents 58-41925, for example)
ii) The direction of the X-ray generator 2 is made unchangeable. The panoramic photographing film cassette 8 is processed so that X-ray can pass through the cassette 8.
In the case of the above-mentioned panoramic/cephalo photographing selection method i) of a prior art, the following operation steps are required when switching the panoramic photographing mode to the cephalo photographing mode. The rotary arm 1 must be rotated so that the panoramic photographing film cassette 8 is located outside the irradiation range of the X-ray. The X-ray generator 2 must then be directed to the cephalo photographing film cassette 91. The slit disposed in front of the X-ray generator 2 must be replaced with that for cephalo photographing. (The slit for panoramic photographing must be used when switching the cephalo photographing mode to the panoramic photographing mode). These operation steps are done manually and thus troublesome and may cause errors since many components are related to the selection. With a first example of the selection means ii) of the prior art, the panoramic photographing film cassette 8 is rotatable so that the cassette 8 can be located outside the X-ray irradiation range during cephalo photographing. With a second example of the selection means ii) of the prior art, an opening for passing X-ray can be formed in the cassette 8 so that X-ray can be irradiated to the cephalo photographing film cassette 91 through the opening during cephalo photographing. In the case of the first example, the center of the rotation must be set at the end of the cassette support section. This makes the rotation parts larger and heavier. The rotation support section must thus be made stronger. In addition, the cassette 8 must be driven during panoramic photographing. Therefore, the mechanism for driving the cassette 8 must also be rotated. This makes the structure of the example very complicated. In the case of the second example, the front plate with a slit necessary for panoramic photographing and the rear X-ray protection lead plate must be slid by at least one-third of the cassette support section in order to form the above-mentioned opening. This makes the structure of the slide mechanism complex. In addition, the opening is covered with a sheet to prevent entry of a foreign matter. This may reduce the intensity of X-ray.